Program-selecting circuits



April 3, 1928.

M. E. STRIEBY PROGRAM SELECTING CIRCUITS Filed Dec. 10, 1923 ATTORNEY INVENTOR Patented Apr. 3, 1928.

- UNITED STATES mm- OFFICE.

MAURICE E. B'IBIEBY, OI IIIILBUBN m JERSEY. ABSIGllOB TO. mum m PHONE AND TELEGRAPH COMPANY, A CORPORATION 01', NEW YORK,

rnoem-mnc'rmecmcuns. Application filed December 10, 1828. Serial lie. 678,728.

which may be directively controlled by the,

subscriber to connect the terminals of the subscribers line to the terminals of any one of a number of trunks each leading to a different program.

By the use of a directlvely controlled selective switch for selecting a. program, -it

becomes immaterial whether the programbe transmitted at volce frequencies or carrier frequencies, and it also becomes immaterial Whether the several programs be transmitted at the same frequency or whether dlfferent carrier frequencies are used for different programs. The directive switch may be controlled by impulses ofeither direct or alternating current and the source of current for operating the switchesmay be located either at the sendin station or at the subscribers station. Pregerably, the directive switch, in accordance with the present invention, will be operated by an impulse sender at the subscribers station over th two s des of theline in parallel.

The invention will now be more fully understood from the followin description, when read in connection wit the accompanying drawing, Figure 1 of which illustrates how a direct current operated direc tive switch. may be used to select. a program,

transm tted at ordinary telephonic frequencies; Fig. 2 of which shows how a similar switch may be used to select carrier frequency programs; Fig. 3 of which shows how a directive switch operated by alternat ing current may be used to select voice frequency programs, and Fig. 4 of whlch shows how a similardirective switch may be used to select carrier frequency programs.

Referring to Fig. 1, L designates an ordimay comprise two windings, th

nary telephone transmission line terminatmg in the usual subscribers set S at one end and terminating at the central ofiice in the usual switching jack J. Normally the telephone line L is connected over the contacts of a cut-off relay CO to the windings of the line relay LR. The line relay, as is usual e upper oi side of the which is associated with the tip The lower winding line and is inductive. is associated with the and is non-inductive, and consequently, does not magnetizethe core of the relay. when current flows through. said winding, The

ring side of the line cut-off relay CO is so arran ed'that when it is operated the line relay L is disconnected from the hue L andt e line is connected directly to the tip and ring terminals of the jack J.

In order that the line ma be used for program purposes during sue time as it is not being used for ordinary telephone urposes, a program receiver such as the end speaker LS is provided at the subscribers station. This receiver is bridged across the line through the back contacts 14 and 15'of the subscribers switchhook. When the substation set S is used for ordinary telephonic purposes, the removal of the receiver from the switchhook opens the circuit of the loud speaker L S so that it may not be then used for receiving programs." At the central oifice a pair of conductors 11 are connected from the back contacts of the cut-ofi relay CO to the Wipers 12 of the directive switch DR.

The switch DR may be stepped by means of the stepping magnet SM into connection with any one of a number of trunks A, B, C

or D, leading to different voice frequencyprograms.

In order to operate the stepping magnet SM, a switching device such as a dlal or key K is provided at the subscribers station for sending impulses of current over the two sides of the line in parallel to operate the differential stepping relay SR, the relay SR being bridged across the conductors leading from the back contacts of the cut-off relay in parallel with the windings of the line relay LR.- The circuit of the key K is connected to the midpoint of the brid ed impedance 16, this impedance being ridged across the conductors leading to the land speaking receiver LS. The impedance 16 is shownin Fig. 1 as a ure resistance. It may, however, also contam inductance thereby causing a smaller loss to the voice frequenc currents in the circuit "across which it is ridged. Consequently, when the receiver is removed from the switchhook, the impedance of the bridge 16 is disconnected from the line. The impulses transmitted over the two sides of the line to operate the stepping relay SR are direct current impulses and may be supplied from a direct current source located either at the central oifice or at the subscribers station as indicated.

The operation is as follows: When the line L is not in use for telephone purposes and the subscriber desires to hear a program, such as the program C, for example, the subscriber will merely actuate the dial or ke K, thereby sendin impulses from groun through said key, thence in parallel through the bridge 16, over the contacts 14 and 15 of the switchhook 10, over the two sides of the line L, over the upper and lower back contacts of the cut-off relay CO, and through the u per and lower windings of the differentia stepping relay SR, at which point the parallel circuit merges and passes over conductor 17 to battery. It will be observed that a path is established from ground, over the key K, through the left-hand half of the bridge 16, then over the tip conductor of the line L, upper back contact of the cutoff relay CO, and through the upper winding of the line relay LR to battery. The

resistance of the element 16 is so great, however, that the line relay is not operated over this circuit. The current flowing through the two windings of the differential relay SR, however, operates said relay so that the impulses sent by the key K are transmitted by the relay SR to the stepping magnet SM. Accordingly, the directive switch DR is operated step-by-stepbythe mechanism conventionally indicated to advance the wipers 12 to the terminals of the trunk leading to the program G. The currents for this program are now transmitted over the wipers 12 and conductors 11, overthe back contacts of the cut-oflt' rela CO and over the line L to the loud spea er LS.

If, while the circuit is being used for program purposes, the subscriber desires to make a telephone call, he merely removes the receiver from the switchhook 10 in the usual manner. The loud speaker LS is disconnected at the back contacts 14 and 15 the line L, over the switchhook 1O,v back causes the line relay to operate the line lamp (not shown) in the usual manner.

The operator, upon observing this signal, will insert the plug of the cord' circuit into the jack J thereby actuating the cut-off relay CO. The cut-01f relay connects the line L at its front contacts to the tip and ring terminals of the jack J, and at the same time disconnects the line L from the relay LR and the differential relay SR, as well as the broadcasting connections 11 leading to the switch DR. The call is then completed in the usual manner. At the end of the conversation, the subscriber hangs up his receiver and the operator withdraws the plug from the jack J, thereby releasing the cut-off relay CO. This at once connects the line L to the program connections 11 and the subscriber may continue to hear the program being transmitted. v

If, while the program is being received, a telephone callshould come in for line L, the operator will insert the plug of her cord into he jack J, thereby operating the cut-off relay as before. The line L will now be disconnected from the program and will be connected over the front contacts of the cutoff relay to the terminals of the jack J. In answer to the ringing signal, the subscriber will remove his receiver from the switchhook and disconnect the loud speaker LS and the bridge 16. It will be observed that ifthe line is being used for telephonic purposes, it is impossible to set the directive switch DR, for the key K and the bridge 16 are disconnected at the subscribers station as soon as the subscriber removes his rerier frequencies, it is to be observed that the line may be used simultaneously for receiving program transmission and for ordinary telephonic purposes. Consequently, the con nections 11 extending to the wipers 12 of the directive switch are extended to the tip and ring sides of the line L adjacent the armature connections of the cut-01f relay, so that the operation of the cut-01f relay will not disconnect the program connections 11 from the line L, the cut-ofi relay in this instance merely serving to disconnect the line relay LR and the stepping relay SR.

. key

messes j that the telephone set is in use, it being undesirable to permit change of program at this time because the subscriber would hear the noise due to the pulses transmitted by the ke K. Y I The carrier frequency programs may be. transmitted each at a different frequency,

but by the use of the directive selective switch it is possible to use the same carrier frequency for all of the programs, since but one program will be transmitted over a line at a time. At the subscribers station it will, of course, be 'necessa to provide suitable amplifying and detecting apparatus conventionally indicated at AD in order to translate the carrier program into voice frequency currents for operating the loud speaker.

' of Whether the same carrier used for all of the programs or whether a No selecting apparatus is necessary at the subscribers station even in the case of carrier transmission, except a single high pass filter conventionally indicated at HP, this filter being provided to prevent the voice freuency current-s transmitted over the line rom actuating the loud speaker. The high ass filter will, of course, pass the carrier requencies used for broadcastin regardless equency 1s difierent carrier frequency is used for each program.

Instead of emplo ing direct current for operating the selective switch, pulses of a1- ternating current may be emplo ed as indicated in Fig. 3. In this figure t e circuit is arranged for the selection of voice frequency programs. Consequently, the connection of the loud speaker LS to the line and the connection of the conductors 11 to the line will be the same as inFig'. 1 The relay SR, however, will be a differential alternating current relay instead of adirect current relay. The windings of the relay SR will be connected to the generator G or ground, as the case may be, through condensers 17 provided for the purpose of keeping-the direct current out of the ground connection. These condensers may be included in conductors common to a large number of relays, such as LR, associated with the different lines. At the subscribers station the connections through the key K to the two sides of the line willbe made through a'pair of condensers 18, said condensers being arranged to bridge across the loud speaker LS when the switching key K is depressed.

The source of alternatin current for oper rating the directive switch Rymay be either at t e central station or at the subscribers .crstation. As indicated in the figure, the switch 16 may be thrown to its upper positron, thereby connecting the alternating current source G to the windings of the rela SR. A similar switch 16' at the subscriber s station, when thrown to its u per position,

will connect the circuit of t e key K to ground. 13y reversing the connections of the two switches, the key K. will be connected to ground through an alternatingcurrent source G at the 'subscribers station, while the wlndings of the relay SR will be connected directly to ground at the central station.

The alternating current used for operating I the directive switch DR may have any desired frequency but it will usually be expedient to use currents supplied from the' power mains of a lighting circuit. This frequency usually is a ut 60 cycles but as the ringer of the subscribers set is usually tuned to a frequency of about 20 cycles, the ringer will not respond to the ton of the alternating current for operating the directive switch. p

In order to select a desired pro m, the subscriber manipulates the key l t hereby completing a circuit (assuming the switches are in their upper position) from ground, to the midpoint of the condensers 18, thence in parallel through said condensers, over the ack contacts 14.- and 15 of the switch-hook 10, over the two sides of the line L in parallel, over the back contacts of the-cut-ofi" relay 00, through the upper and lower windings of the stepping relay SR, through the two condensers 17 to the point 19, and thence to ground through the source G. Each time the key K is closed, the alternating current rela transmit a pulse so t at the directive switch is actuated step-by-step until its wipers rest SR is energized to,

the desired program. The line relay LR will, of course, not be actuated by the alternating current, partly because its lower winding, through which the alternating cur rent flows, is non-inductive, and partly because its circuit is not tuned to the frequency of the alternating current. The remaining features of the operation are as already described in connection with Fig. 1.

The alternating current arrangement may be employed for selecting carrier frequency programsas illustrated in Fig. 4. As in the case of Fig. 2 the program connections 11 are made directly to the terminals of the line L so that the operation of the cut-off relay does not disconnect the broadcasting circuit. The tuned circuits including the key K at the subscribers station and the differmany other organizations widely difl'erent central ofiice are connected to the two line conductors in the same manner as in Fig. 2, so that the impulses will be transmitted over the line conductors in parallel and so that the selection of programs may take place while the line is being used for telephonic purposes. The loud speaking receiver LS, together with the amplifying detector AD and the high pass filter HP, will, as in Fig. 2, be bridged across the line L directly, independently of the switchhook. Consequently, a. program already selected may contmue to be received by the subscriber through his loud speaker while a conversation is taking place, although the subscriber-will not be able to change the program. The operation of the circuit in detail will be clear from the previously described o eration of Figs. 2 and 3 and need not be urthe-r discussed.

It will be obvious that the general principles herein disclosed may be embodied in from those illustrated without departing from the s irit of the invention as defined in the following claims.

What is claimed is:

1. In a program transmitting system, a subscribers telephone line terminating in a subscribers telephone apparatus at the subscribers station, switching means at the central ofiice whereby? a connection. may be established between said subscribers line and another subscribers line, a plurality of trunks atthe-central ofiice upon which programs may be impressed, a .directively operated switch independent of said first mentioned switching means at the central office for establishing connections between said line andany desired trunk to exclusion of other trunks, and means at the subscribers station for controlling the operation of said switch over the two sides of the line in parallel with the receiver on the switch hook.

2. In a program transmitting system, a subscribers telephone line termlnating in a subscribers telephone apparatus at the subscribers station, switching means at thecentral ofiice whereby a connection may be established between said subscribers line and another subscribers line, a plurality of trunks at the central office upon which programs may be impressed, a step-by-step switch independent of said first mentioned switching means at the central office for establishing connections between said line and any desired trunk to exclusion of other trunks, and means at the subscribers station for operating said switch over the two sides of the line in parallel with the receiver on the switch hook.

3. In a program transmitting system, a subscribers telephone line terminating in a subscribers telephone apparatus at the sub-1 scribers station, switching means at the central otfice whereby a connection may be established between said subscribers li e and another subscribers line, a plurality of trunks at the central ofiice upon which programs may be impressed, an impulse-operated switch independent of said first mentioned switching means at the central office for establishing connections between said line and any desired trunk to exclusion of other trunks, an impulse sender at the subscribers station, and means whereby said sender may transmit impulses over the two sides of the line in parallel to operate said switch with the receiver on the switch hook. 4. In a program transmitting system, a subscribers telephone line terminating in a subscribers telephone apparatus at the subscribers station, switching means at the central office for establishing connections between said line and other lines so that telephone conversations may take place at ordinary telephonic frequencies, a plurality of trunks at the central ofiice upon-which different programs may be impressed at carrier frequencies, a directively operated switch independent of said first mentioned switching means at the central office for switching, said subscribers line to the trunk upon which a desired carrier rogram is impressed to exclusion of ot ler trunks, and means at the subscribers station to control the operation of said switch over the two sides of the line in parallel with the receiver on the switch hook.

5. In a program transmitting system, a subscribers telephone line terminating in a subscribers telephone apparatus at the subscribers station, switching mean at the central ofiice for establishing connections between said line and other lines so that telephone conversations may take place at ordinary telephonic frequencies, a plurality-of trunks at the central office upon which different programs may be impressed at carrier frequencies, a step-by-step switch independent of said first mentioned switching means at the central office for switching said subscribers line to the trunk. upon which the desired carrier program is impressed to exclusion of other trunks, and means at the subscribers station for controlling the operation of said switch over the two sides of the line in parallel with the receiver on the switch hook.

.6. In a program transmitting system, a subscribers telephone line terminating in a subscribers telephone apparatus at the subscribers station, switching means at the central office for establishing connections between said line and other lines so that telephone conversations may take place at ordinary telephonic frequencies, a plurality of trunks at the central ofiice .upon which different programs. may be impressed at carrier frequencies, an impulse-operated switch independent of said first mentioned switchin means at the central ofiice for switching sai subscribers line to the trunk upon which a. desired carrier program is impressed to ex- 5 clusion of other trunks, an impulse sender at the subscribers station, and means for transmitting impulses from said sender to said switch over the two sides of the line in parallel with the receiver on the switch hook. 10 In testimony whereof, I have signed my name to this specification this 7th day of December, 1923.

, MAURICE E. STRIEBY. 

